The long-term research goal is to understand how neural systems respond to changing external conditions. Sensory cells are important in this process as they encode information about specific aspects of an organism's environment. An interesting question is how the presence of neuromodulators affect the encoding of sensory information. The crab STG is an ideal preparation for such a study, since post-synaptic targets of the GPR sensory cell can be easily accessed and there is a long history of studying neuromodulation in this system. By the conclusion of my research plan, I will be able to pose a very important and neglected question that should interest anyone who studies coding: If the affect of neuromodulators is to create multiple "encoders" of sensory information, how does the target of the information know which "decoder" to use and when? I propose to: 1. Record GPR activity in a semi-intact animal. 2. Measure modulation of GPR stretch response; determine whether GPR itself is modulated. 3. Characterize the encoding of muscle stretch into spikes and its modulation. 4. Decode spike trains to determine muscle strength. 5. Characterize the responses of STG neurons to GPR activity.